The present invention relates to a reactive sputtering apparatus to be used in the process of manufacturing an object such as a semiconductor or an electronic component.
In a reactive sputtering apparatus, reactive gas such as nitrogen gas is added to a discharge gas such as argon gas used in a normal sputtering apparatus so as to deposit a compound, formed by the reaction of the reactive gas with particles sputtered from the material of a target, in the form of a thin film on a substrate.
Since a reactive sputtering apparatus is capable of easily forming various kinds of thin films merely by introducing reactive gas into a normal sputtering apparatus, the reactive sputtering apparatus is preferably used in the process of manufacturing a semiconductor or an electronic component.
An example of a conventional reactive sputtering apparatus is described below with reference to FIG. 6.
The reactive sputtering apparatus comprises a vacuum chamber 1; a vacuum discharge opening 2 for evacuating air from the chamber 1; a gas-introducing pipe 3 for supplying discharge gas 5 and reactive gas 6 into the chamber 1; a gas flow rate controller 4 for controlling the flow rate of the discharge gas 5 and the reactive gas 6; a target 7 mounted on a cathode 8; a power source 9 for applying a voltage to the cathode 8 fixed to the inner surface of the chamber 1; a magnetic circuit 10, mounted in the cathode 8 and having a center circular magnet 10a and an annular magnet 10b, for generating a magnetic field; a substrate holder 11 to which a substrate 12 is secured; and an erosion region 13, of the target 7, in which plasma density is highest during magnetron discharge. The erosion region 13 is located between the magnets 10a and 10b. The target 7 is located below the magnets 10a and 10b in the cathode 8.
The operation of the reactive sputtering apparatus of the above-described construction will now be described below with reference to FIG. 6. First, air is evacuated from the chamber 1 by a vacuum pump (P) through the vacuum opening 2 to a degree of vacuum as high as approximately 10.sup.-7 Torr. The discharge gas 5 and the reactive gas 6 are introduced into the chamber 1 through the gas-introducing pipe 3 connected with the chamber 1, with the quantity of the discharge gas 5 and the reactive gas 6 being controlled by the gas flow rate controller 4.
The pressure inside the chamber 1 is kept at 10.sup.-3 to 10.sup.-2 Torr. A negative voltage is applied by the power source 9 to the magnetron cathode 8. Plasma is generated by magnetron discharge in the vicinity of the surface of the target 7 under the action of a magnetic field generated by the magnetic circuit 10 disposed inside the cathode 8 and that of an electric field generated by the power source 9. A compound formed as a result of the reaction of particles sputtered from the target 7 with the reactive gas 6 is deposited in the form of a thin film on the substrate 12 fixed to the substrate holder 11.
It is known that sputtered particles and the reactive gas 6 react with each other mainly on the substrate 12.
According to the conventional reactive sputtering apparatus, the discharge gas and the reactive gas are supplied into the chamber through the same gas-introducing pipe. As a result, the reactive gas exists not only in the vicinity of the substrate 12 but also in the erosion region of the target in which plasma density is highest in magnetron discharge. Consequently, a compound formed as a result of the reaction of the material of the target with the reactive gas deposits on the surface of the target. The compound greatly prevents particles from being sputtered from the target. Therefore, the thin film is formed on the substrate at a speed of 1/3 to 1/5 the speed at which a thin film is formed by a normal sputtering apparatus.